A Conchological Manual, George Brettingham Sowerby [little readers .TXT] 📗

distinguished as follows:

 

CHITON. Composed of eight valves; valves contingent. Fig. 227.

 

CHITONELLUS. The same, with the valves distant. Fig. 228.

 

PATELLA. Conical, symmetrical. Fig. 229, 230.

 

PATELLOIDA. Differing from Patella in the animal. Fig. 231.

 

SIPHONARIA. With a siphon on one side. Fig. 231*.

 

SCUTELLA. Siphon close to the side of the head. Fig. 510, 511.

 

   PHYLLONOTUS. Sw. A sub-genus of Murex, thus described: "Canal moderate;

   varices foliated, laciniated, compressed, or resembling leaves;

   inflatus. Mart. 102. fig. 980, eurystoma. Zool. Ill. ii. 100.

   imperialis. Ib. pl. 109." Sw. p. 296.

 

   PHYSA. Drap. A genus formed for reversed species of Limnæa, Auct. Fig.

   310, P. castanea.

 

   PHYSETER. Humph. SOLARIUM, Lam.

 

   PILEOLUS. Cookson. (_A little cap._) _Fam._ Neritacea, Lam.--_Descr._

   Patelliform, with the apex sub-central, straight. In the lower disc, or

   under surface, the centre of which is rather raised or cushion-shaped,

   is placed the lateral, narrow, semilunar aperture, with the outer lip

   marginated and the inner lip crenulated.--_Obs._ This interesting genus

   is known only in a fossil state. Two species are found in the upper

   layer of Oolite, above the Bradford clay. The spire, although internal,

   connects this genus in some degree with Neritina. Still there is no

   danger of confounding them. Fig. 332, P. plicatus.

 

   PILEOPSIS. Lam. CAPULUS, Montf.

 

   PILLAR. The usual English name for the column which forms the axis of

   spiral shells, around which the whorls revolve. See COLUMELLA.

 

   PINNA. Auct. (_The fin of a fish._) _Fam._ Mytilacea, Lam.--_Descr._

   Equivalve, inequilateral, oblique, wedge-shaped, thin, horny; umbones

   terminal; hinge rectilinear, without teeth; anterior margin sinuated,

   to admit the passage of a byssus; posterior margin truncated, gaping;

   muscular impressions two in each valve; posterior large, sub-central;

   anterior small, terminal, sometimes double.--_Obs._ The beautiful large

   shells of which this genus is composed, are possessed of a large,

   flowing, silky byssus, of which gloves and hose have been manufactured.

   They have received their name from their resemblance to the pectoral

   fins of some fishes. Some species attain very large dimensions, and

   measure two feet in length. A very improbable story is told with regard

   to animals of this genus, namely that a certain small species of crab

   is in the habit of taking refuge from its enemies in the shell of the

   Pinna, into which it is received with great hospitality and kindness by

   the "_blind slug_," which inhabits it. In return for which kindness, he

   occasionally goes abroad to procure food for both. On his return he

   knocks at the shell, which is opened to receive him, and they share the

   supplies together in convivial security! Some species are smooth,

   although the greater number are imbricated or crisped outside. P.

   saccata, fig. 162.

 

   PINNATED. (From _Pinna_, a fin.) When a part of a shell is spread out

   and smooth, as in Rostellaria columbaria, fig. 403, it is said to be

   _alated_, or winged, but when the part which is spread is radiated or

   ribbed, like the fin of a fish, it is _pinnated_, as in Murex pinnatus,

   and Murex tripterus. (Conch. Illustr.)

 

   PIRENA. Lam. A genus of fresh-water shells, rejected by De Ferussac and

   other authors, who place Lamarck's two first species with Melanopsis,

   and his two last with Melania. Fig. 316, P. terebralis.

 

   PISIDIUM. Leach. A genus of river shells separated from Cyclas

   principally on account of a difference in the animal. The species of

   Pisidium, however, are less equilateral than the Cyclades, and the

   posterior or ligamentary side of the latter is the longer, while that

   of the former is the shorter. Fig. 112.

 

   PISIFORM. (_Pisum_, a pea; _forma_, shape.) Shaped like a pea or small

   globular body.

 

   PISUM. Megerle. (_A pea._) PISIDIUM, Leach.

 

   PITHOHELIX. Sw. A sub-genus of "Geotrochus," Sw. Sw. p. 332.

 

   PITONELLUS. Montf. ROTELLA, Auct.

 

   PLACENTA. Schum. PLACUNA, Auct.

 

   PLACENTULA. Schum. A genus of microscopic Foraminifera.

 

   PLACUNA. Brug. ([Greek: plakous], _placos_, a cake.) _Fam._ Ostracea,

   Lam. and Bl.--_Descr._ Compressed, thin, equivalve, nearly equilateral,

   planorbicular, fibrous, foliaceous; hinge flat, with two diverging ribs

   in one valve, and two corresponding grooves in the other, containing

   the cartilage; muscular impressions one, large, circular, central, and

   one or two smaller in each valve.--_Obs._ The two best known species of

   this well defined genus are the P. Placenta, commonly called the

   Chinese Window Shell, and the P. Sella, called the Saddle Oyster, from

   the anterior margin being turned up so as to resemble a saddle. The

   genus may be known from all others by the diverging costa on the hinge.

   Placunanomia is the only genus resembling it in this respect, but this

   is easily distinguished by a perforation through the shell. Fig. 184,

Placuna. These shells are used in China to glaze windows.

 

   PLACUNANOMIA. (Sw. _Placuna_ and _Anomia_.) _Fam._ Ostracea, Lam. and

   Bl.--_Descr._ Thin, foliaceous, compressed, sub-equivalve,

   sub-equilateral, irregular, flat near the umbones, plicated towards the

   margins, attached by a bony substance passing through a fissure in the

   lower valve; hinge flat, with two diverging ribs in one valve,

   corresponding with two diverging grooves, containing the cartilage, in

   the other; muscular impressions one in each valve, central,

   sub-orbicular.--_Obs._ The specimens from which Mr. Broderip described

   this singular genus, were brought by Mr. Cuming from the gulf of Dulce

   in Costa Rico. Another species is from one of the Philippine Islands.

   They partake of the characters of several genera, having the hinge of

   Placuna, and being attached by a process passing through the lower

   valve, like Anomia. P. Cumingii, fig. 189.

 

   PLAGIOSTOMA. Sow. Min. Con. ([Greek: plagios], _plagios_, oblique;

   [Greek: stoma], _stoma_, mouth.) _Fam._ Pectenides, Lam.

   Palliobranchiata, Bl.--_Descr._ Sub-equivalve, inequilateral, oblique,

   auriculated on each side of the umbones, radiately striated; hinge

   straight in one valve, with a triangular notch in the other.--_Obs._

   This genus, one species of which is spinous, and another smooth, is

   only known in a fossil state. It is found in the Lias and chalk. Fig.

   176, P. spinosum.

 

   PLAIT or FOLD. A term applied to the prominences on the columellar lip

   of some univalve shells, particularly in the sub-family of Volutidæ.

   _Ex._ Voluta, fig. 433; Cymba, 434; and Melo, fig. 435.

 

   PLANARIA. Brown. A minute fossil resembling Planorbis in appearance,

   but differing in being a marine shell, and having a reflected outer

   lip. P. nitens, fig. 312, from Lea's Contributions to Geology.

 

   PLANAXIS. Lam. (_Plana_, flat; and _axis_.) _Fam._ Turbinacea, Lam.

   Entomostomata, Bl.--_Descr._ Sub-ovate, pyramidal, solid; spire

   measuring ½ or 1/3 of the axis, consisting of few whorls; columella

   contiguous to the axis, flat, truncated, and separated from the outer

   lip by a short canal; outer lip thickened and denticulated within;

   operculum horny, thin, with a terminal nucleus.--_Obs._ This is a genus

   of small marine shells found in the West Indies, &c. Fig. 365, P.

 sulcata.

 

   PLANE. (_Planus._) Flat, planed, as the columellar lip of Purpura, fig.

   414.

 

   PLANORBICULAR, (_Planus_, flat; _orbis_, an orb.) Flat and circular, as

   Ammonites, fig. 478.

 

   PLANORBIS. Müll. (_Planus_, flat; _orbis_, an orb.) _Fam._ Lymnacea,

   Lam. and Bl.--_Descr._ Thin, horny, convolute, planorbicular, nearly

   symmetrical; spire compressed, concave, consisting of numerous

   gradually increasing whorls, which are visible on both sides; aperture

   transversely oval, or nearly round; peritreme entire; outer lip thin;

   inner lip distinct, spread over a part of the body whorl.--_Obs._ This

   is a genus of shells abounding in all climates in ditches and stagnant

   pools, not liable to be confounded with any other, excepting the

   discoidal species of Ampullaria, which may be distinguished by the

   aperture being broadest in the opposite direction. It is further to be

   remarked that the discoidal Ampullariæ are dextral shells, and the

   Planorbes are sinistral or reversed; and although the latter are

   sometimes so flat and orbicular that it is difficult to know which is

   the spiral side, it may nevertheless always be ascertained by a careful

   examination. Fossil species are found in the freshwater strata of the

   Isle of Wight, and the neighbourhood of Paris. Fig. 311, P. corneus.

 

   PLANORBULINA. D'Orb. A genus of microscopic Foraminifera.

 

   PLANULACEA. Bl. The second family of Cellulacea, Bl. The microscopic

   Foraminifera contained in this family are described as very much

   depressed, not spiral, chambered, cellular, and having the septa

   indicated by grooves on the external surface of the shell, which

   increase in length from the apex to the base: some of the small

   cellular cavities are to be seen on the margins. This family contains

   the genera Renulina and Peneroplis.

 

   PLANULARIA. Defr. PENEROPLIS, Montf. A genus of microscopic

   Foraminifera.

 

   PLANULINA. D'Orb. A genus of microscopic Foraminifera.

 

   PLANULITES. Lam. DISCORBITES of the same author. A genus of microscopic

   Foraminifera.

 

   PLATIRIS. Lea. ([Greek: platus], _platus_, wide; [Greek: iris],

   _iris_.) A genus including several species of Nayades, referred to

   IRIDINA, Lam. The genus Platiris is divided into two sub-genera.

   Iridina, species which have crenulated margins; I. Ovata, I. exotica,

   Spatha, Lea; those with smooth or very slightly crenulated hinges, S.

   rubeus, S. Solenoides, Mycetopus, D'Orb. Fig. 151.

 

   PLATYLEPAS. ([Greek: platus], _platus_, wide; [Greek: lepas], _lepas_,

   rock.) _Order._ Sessile Cirripedes, Lam. _Fam._ Balanidea,

   Bl.--_Descr._ Conical, depressed, consisting of six valves, each

   divided internally by an angular plate jutting from the centre (like

   the buttress of a wall); operculum consisting of four valves in

   pairs.--_Obs._ This genus differs from Balanus, Coronula, &c. in the

   internal structure of the valves. De Blainville's description of

   Chthalamus partly agrees with this. Fig. 19.

 

   PLECTOPHORUS. Fer. ([Greek: plêktron], _plectron_, spur; [Greek:

   phoreô], _phoreo_, to carry.) A genus consisting of small testaceous

   appendages fixed on the posterior extremity of a species of slug. P.

   corninus, fig. 260.

 

   PLEIODON. Conrad. IRIDINA, Lam. _Fam._ Nayades, Lam.

 

   PLEKOCHEILUS. Guild. AURICULA Caprella, Lam. CARYCHIUM undulatum,

   Leach. (CAPRELLA, Nonnull.) This proposed genus is described as

   scarcely umbilical, dextral, oval, spiral; with the spire elevated,

   obtuse; the two last whorls very large, ventricose; aperture entire,

   elongated; columella with a single plait; the plait concave, inflected.

   Fig. 522, 523.

 

   PLEUROBRANCHUS. Cuv. ([Greek: Pleura], _pleura_, the side; _Branchiæ_,

   gills.) _Fam._ Semiphyllidiana, Lam. Subaplysiacea, Bl.--_Descr._

   Internal, thin, haliotoid, slightly convex towards the spiral apex;

   aperture entire.--_Obs._ This is a very light shell, delicately

   coloured, resembling Aplysia, but differing in the integrity of the

   margin. Fig. 232, P. membranaceus.

 

   PLEUROCERUS. Rafinesque. A genus very imperfectly described in the

   "Journal de Physique" as "oval, or pyramidal; aperture oblong; outer

   lip thin; inner lip truncated at the columella, which is smooth and

   tortuous, not umbilicated. Operculum horny or membranaceous." De

   Blainville, in giving this description, remarks that he has neither

   seen the animal nor the shell of this genus, which he imagines to have

   been formed from the "Paludine Coupée de M. Say."

 

   PLEURORYNCHUS. Phillips. ([Greek: Pleura], _pleura_, the side; [Greek:

   runchos], _rynchus_, a beak.) A genus founded upon a very singular

   species of CARDIUM, distinguished by the short anterior side, and the

   elongation of the hinge line into auricular processes, which are

   truncated at the extremities. C. Hibernicum from the Black Rock near

   Dublin, which is vulgarly called Asses-hoof, and C. elongatum (Sow.

   Min. Con. vol. I. 82.), form part of this genus.

 

   PLEUROTOMA. Lam. _Fam._ Canalifera, Lam. Siphonostomata, Bl.--_Descr._

   Fusiform, thick, in general ribbed or striated transversely; aperture

   oval, terminating anteriorly in an elongated canal; outer lip thin,

   with a fissure near its spiral extremity; columella smooth, nearly

   straight. Found principally in tropical climates.--_Obs._ This genus,

   which nearly resembles Fusus in other respects, may be known by the

   notch in the outer lip. The species differ in the length of the canal.

   Swainson has designated this genus a family, thus divided into genera:

   Brachytoma, in the description of which he says that the spire and

   aperture are of equal length, including the species strombiformis:

   Pleurotoma, in which the channel is so much lengthened, as to be little

   shorter than the spire: Clavatula, having the long narrow slit of

   Pleurotoma, but with a very short canal: Clavicantha, having the canal

   equally short, but the sinus or notch, instead of being linear and

   long, is short and wide; the surface is rough, and the whorls either

   coronated with prickles, or with compressed nodules resembling spines:

   Tomella, which has the spire and canal fusiform, but the spire of very

   few whorls, and the inner lip considerably thickened within where it

   joins